Calcium-silicate-hydrate

Brunauer and co-workers [129, 130] found values of of 1310, 1180, and 386 ergs/cm for CaO, Ca(OH)2 and tobermorite (a calcium silicate hydrate). Jura and Garland [131] reported a value of 1040 ergs/cm for magnesium oxide. Patterson and coworkers [132] used fractionated sodium chloride particles prepared by a volatilization method to find that the surface contribution to the low-temperature heat capacity varied approximately in proportion to the area determined by gas adsorption. Questions of equilibrium arise in these and adsorption studies on finely divided surfaces as discussed in Section X-3. 

Table 6. Calcium Silicate Hydrates Formed at Elevated Temperatures ...

AfwiUite can also be formed, and appears to be the thermodynamically stable calcium silicate hydrate in pure systems, at room temperature. 

Calcium selenite, 22 73t Calcium silicate(s), 12 63 hydration, 5 475-477 Calcium silicate hydrate, 5 477t hydration, 5 475... 

When anhydrous cement mix is added to water, the silicates react, forming hydrates and calcium hydroxide. Hardened Portland cement contains about 70% cross-linked calcium silicate hydrate and 20% crystalline calcium hydroxide. 

The C3A phase is subjected to competitive reaction between water and gypsum to form a small amount of the initial C3A hydrates covered by a protective coating of ettringite, and also a proportion of the C3S hydrates to form a calcium silicate hydrate of low calcium content in the region of 100 nm thick. 

During this phase the initial self-retarding calcium silicate hydrate layer appears to break down, allowing further hydration products from the C3S and C2S phases to be formed. These appear to be produced in three... 

In the presence of calcium lignosulfonate [58], the calcium silicate hydrate gel from the C3S and C2S... 

Comparing metal concentrations in the BA with the amount of the different types of waste (household, industrial, etc.) only one poor correlation (R = 0.6) was observed a higher amount of waste coming from the construction sector caused higher CaO contents in the BA. It is likely that in this case Ca-rich CSH phases (calcium-silicate-hydrate) and gypsum account for a higher CaO content in the BA. 

Tits, J., Stumpf, Th., Rabung, Th., Wieland, E. Fanghanel, Th. 2003. Uptake of trivalent actinides (Cm(III)) and lanthanides (Eu(III)) by Calcium silicate hydrates a wet chemistry and time-resolved laser fluorescence spectroscopy (TRLFS) study. Environmental Science and Technology, 37, 3568-3573. 

BONHOWE, I., WlELAND, E., SHEIDEGGER, A. M., Ochs, M. Kunz, D. 2003. EXAFS study of Sn(IV) immobilization by hardened cement paste and calcium silicate hydrates. Environmental Science and Technology, 37, 2184-2191. 

Richardson, I. G. Groves, G. W. 1993. The incorporation of minor and trace elements into calcium silicate hydrate (C-S-H) gel in hardened cement pastes. Cement and Concrete Research, 23, 131-138. 

Rose, J., Moulin, I. et al. 2000. X-ray absorption spectroscopy study of immobilization processes for heavy metals in calcium silicate hydrates 1. Case of lead. Langmuir, 16, 9900-9906. 

Tommaseo, C. E. Kersten, M. 2002. Aqueous solubility diagrams for cementitious waste stabilization systems. 4. Mechanism of zinc immobilization by calcium silicate hydrate. Environmental Science and Technology, 36, 2919-2925. 

Ziegler, F., Giere, R. Johnson, C. A. 2001a. The sorption mechanisms of zinc to calcium silicate hydrate Sorption studies and microscopic investigations. Environmental Science and Technology, 35, 4556-4561. 

CASH CBM CBO CBPC CC CCB CCM CCP CDB CEC CFBC CFC CFR CMM COP CSH CT Calcium aluminosilicate hydrate Coal bed methane Carbon burn-out Chemically-bonded phosphate ceramics Carbonate carbon Coal combustion byproducts Constant capacitance model Coal combustion product Citrate-dithionate-bicarbonate Cation exchange capacity Circulating fluidized bed combustion Chlorofluorocarbon Cumulative fraction Coal mine methane Coefficient of performance Calcium silicate hydrate Collision theory... 

The natural curing reactions that occur in a standard Portland cement involve the formation of calcium hydroxide (portlandite) and Ca(OH)2, as well as calcium silicate hydrate (CSH). Over time, the cement will absorb C02 from the air, converting the Ca(OH)2 and some of the CSH, to calcium carbonate, CaC03, through reactions such as those shown in Figure 15.1 (Siegers and Rouxhet, 1976 Suzuki et al., 1985 Taylor, 1990). Supercritical C02 processing carbonates the calcium hydroxide, removes water from the... 

In the presence of calcium lignosulfonate [58], the calcium silicate hydrate gel from the C3S and C2S phases tends to have a greater proportion of the crumpled foil morphology type than the corresponding system without the admixture. This observation tends to be made only at high concentrations of... 

Mixed oxides have a widespread application as magnets, catalysts, and ceramics. Often, nonstoichiometric mixtures with unusual properties can be prepared for example, Fe203 and ZnO have been milled for the production of zinc ferrite [40], while mixed oxides of Ca(OH)2 and Si02 were described by Kosova et al. [77]. Piezoceramic material such as BaTi03 from BaO and anatase Ti02 has been prepared [78], while ZnO and Cr203 have been treated by Marinkovic et al. [79] and calcium silicate hydrates from calcium hydroxide and silica gel by Saito et al. [80]. The thermal dehy-droxylation of Ni(OH)2 to NiO or NiO-Ni(OH)2 nanocomposites has also been investigated [81]. 

The second part of my talk deals with the surface of a particular solid, a calcium silicate hydrate, called tobermorite. The two main constituents of Portland cements are two calcium silicates, which make up about 75% or more of a portland cement by weight, and both of these silicates produce tobermorite in their reaction with water. This tobermorite is the most important constituent of hydrated portland cement, concrete, and mortar. That is not the reason, however, for my talking about it—the reason is that it is a fascinating substance for a colloid chemist. I will discuss only two properties of the tobermorite surface the surface area and the surface energy. 

Previous investigations of these hydration reactions at room temperature have been reviewed recently (4). Research in this laboratory has included the stoichiometry of the hydration of both silicates, employing different methods of hydration (2, 3, 5, 21), and a determination of the surface energy of tobermorite, the calcium silicate hydrate produced in the hydration of both silicates under most experimental conditions (8). The surface area and the surface energy of tobermorite are briefly discussed by Brunauer (I). These properties play vital roles in determining the strength, dimensional stability, and other important engineering properties of hardened portland cement paste, concrete, and mortar. 

The calcium silicate hydrate formed in both cases appears to be a very poorly crystallized version of the natural mineral tobermorite. The use of the name tobermorite for the calcium silicate hydrate obtained in the hydration of Ca8Si05 and Ca2Si04 is not fully justified nevertheless, because in all publications from this laboratory that name was used, the usage is retained in this paper. 

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